In the current color photographic methods, based on the subtractive color process, it is usually the case where a yellow coupler is added in a blue-sensitive silver halide emulsion layer, a magenta coupler is added in a green-sensitive silver halide emulsion layer and a cyan coupler is added in a red-sensitive silver halide emulsion layer.
The current color photography is based on the reaction in which these couplers are coupled with the oxidation product of the aromatic primary amine-based developing agent in the developer by color development and form azomethine and indoaniline dyes in respective photographic layers.
For obtaining good color reproducibility, it is desirable that the yellow color dye formed by development has an absorption spectrum in the blue region alone while showing no undesirable absorption in the green or red region, the magenta color dye has an absorption spectrum mainly in the green region while showing no undesirable absorption in the adjoining blue or red region, and the cyan color dye shows no undesirable absorption in the green or blue region.
Traditionally, benzoyl acetanilide type couplers and pivaloyl acetanilide type couplers have been in practical use as yellow couplers for negative films and papers, respectively, but further improvements are desired in absorption spectrum and light fastness.
In the case of negative films, it is possible to correct undesirable absorption by masking. On the other hand, no improvement is possible by such a means in the use for color papers; therefore, it is more important to improve the coupler itself. Also, there are some other methods; for example, U.S. Pat. No. 4,774,181 describes a coupler that releases a fluorescent substance, which is based on the idea that the broadness of the absorption spectrum of coloring dye is compensated by some luminescence.
However, none of the conventional fluorescent dyes has satisfactory fastness, and further improvements are needed.